1. Field of the Invention
The present invention relates to a fine fabrication process using a radiation sensitive resist especially a negative type resist in a production of a semiconductor integrated circuit.
2. Description of the Prior Art
As the etching step in the production of semiconductor integrated circuits, a process for forming an etched pattern by using a light sensitive resin which is sensitive to visible ray and ultraviolet ray (photoresist) has been practically employed. Recently, requirements of higher density and higher integration of devices have been increased to improve reliability and characteristics of the integrated circuits. Thus, special studies for development of ultrafine work technology for circuit patterns have been made. In the studies, a process for forming a circuit pattern having high accuracy by exposure of high energy radiation such as deep ultraviolet rays having short wavelength, X ray and electron beam instead of visible light has been developed. Thus, a development of resist having high functional characteristics sensitive to the radiation has been required. In the production of an integrate circuit, a resist is coated on a substrate to form a film and is exposed by the radiation and is developed to form a fine pattern and the layer having the fine pattern on the substrate is etched to remain the pattern forming part. In the step of the production of the integrated circuit, high sensitivity and high resolution are important as functional characteristics required for the resist. A resist corresponding to fine work accuracy in submicron upto 1 .mu.m as the resolution is especailly required. Moreover, a wet etching process using a chemical has been employed in an etching process, however a wet etching process is not suitable in view side etching. In the fine work in submicron, a dry etching process by a gas plasma or a reaction sputtering has been newly employed. Thus, excellent material durable to the dry etching is required as the resist. Certain radiation sensitive resists for fine work have been developed. It is quite small to satisfy with all of the above-mentioned requirements. For example, poly(glycidyl methacrylate) (PGMA) has been known as the negative type resist and it has high sensitivity in the order of 10.sup.-7 C/cm.sup.2 but has unsatisfactory resolution and has not enough dry etching resistance. On the other hand poly(methyl methacrylate) (PMMA) known as positive type resist has large .gamma. value as an index of resolution such as about 2.5 to form a fine pattern in submicron but has a low sensitivy to electron beam in the order of 10.sup.-4 -10.sup.-5 C/cm.sup.2 which is lower than a practical sensitivity and has not enough dry etching resistance though it is superior to that of PGMA. The polymers having an aromatic ring in a repeat unit of a polymer which have satisfactory dry etching resistance, have been known, however, these resists are photoresists which have low sensitivity to radiation.